depends what you are doing and where you are going?
if you are going trekking and staying in tents in say nepal then a down bag with a rating of between -10 to -15 should do the trick. Synthetic bag will be cheaper, bulkier and heavier but essentially do the same job.
there are lots of good brands out there Mountain designs, sea to summit, paddy pallin, exped..the list goes on.

Yep, Nepal. it should be -10 to -5 comfort zone, but it looks like the companies usually cheating about the temperature ratings, that's why i'm looking for some comments.
If someone slept on the snow in a bag with -10 to -5 comfort zone and was not freezing?

On snow? Ideally with two mats under you, yes. One self-inflating and one closed cell foam.

Any of the better reputable brands will do the trick. They do not 'cheat' so much as that there is no gold standard for how to measure temp ratings, in part to be fair, because it is very subjective. Do you sleep hot or cold? Do you need space or can you cope with a very tight mummy bag? etc.

Often the best way to gauge how accurate the rating is, is to look at the fill weight of one brand compared to others. Assuming the fill is of a similar quality (900+ etc). Some brands use the EN 13537 standard such as Marmot and from what I've read this seems to be fairly accurate.

The other thing is to know your own body and whether you sleep hot or cold then use this to determine whether you go a bit overkill on the rating or not.

Western Mountaineering make very good bags. Also remember not to skimp on the mattress. Doesn't matter how warm your bag is if your mattress is crap.

Look at the link below as an example (I actually own this bag and have spent many happy nights on snow here in Aus, things are likely different at 5000m though). The temp ratings are quite broad -3 comfort, -10 limit and -28 extreme as measured by the 13537 rating. So that can serve as a guide, at -10 you're probably not going to have the best sleep whereas at -3 you'll be snug as a bug (depending on the rest of your gear). You can then give yourself a little leeway depending on whether you're a hot or cold sleeper. If you're a cold sleeper for example, you might want the model up which has a comfort of -7 instead. As others have said, mattresses count for a lot and remember you can also use a liner to give the bag a little extra warmth.

There are heaps of brands around and things can get pricey, so do your homework, read reviews and work out which one fits your needs for the best price. Don't skimp on quality either, you won't have a good time if you're uncomfortable.

On 22/01/2013 UILKA wrote:>Yep, Nepal. it should be -10 to -5 comfort zone, but it looks like the>companies usually cheating about the temperature ratings, that's why i'm>looking for some comments.>If someone slept on the snow in a bag with -10 to -5 comfort zone and>was not freezing?

Bizarre to say that companies cheat with ratings, you are aware that one of the most important factors in how warm you feel is YOU, which sadly the bag manufacturers can't always cater for.

If you're a cold sleeper, which from the sounds of it you are, then look at any rating as optimistic, believe it or not it's not the manufacturers' fault, and our experience of being warm or otherwise will NOT help you. I regard most ratings as pessimistic and am warm at 5 degrees lower than the bags are rated as comfortable, so me giving you an opinion would be useless.

The advice about having a cheap foam mat and another decent mat is a good one though. If I'm carrying I prefer just one good mat, if someone else is carrying then a cheap foam mat as well is a good thing.

PS the original post about being warm at 5,000 meters was also rubbish, there's a world of difference camping at 5,000 meters on Denali in winter compared to 5,000 meters at Kilimanjaro in late summer and you'd get totally different recommendations.

Your matt that you sleep on will play a big part.. I hard a 3/4 thermarest .. and when camping on snow (at alititude) I had to put my feet into my backpack and 'pad' them so my legs were nt touching the ground.. as soon as I came off my matt.. I woke up.. but I saved some wieght and space.. might go for those down filled matts when I win tatts..

Get a liner - cotton/silk or other .. this will extend the life of your bag.. as the frequency you have to wash it will (hopefully) reduce..

I have also tried a lighter sleeping bag (was a artificial down.. el cheapo).. and then just slept in all my thermals & down jacket.. mainly used it for Alpine ascent .. super lightweight... but found it was nt terribly successful.. waking up at 3 am (instead of 4 am) and being cold just to save 150 grams?

My two bags for altitude (Paddy Pallin Twynam & Mont somethingorother) have about 1000g of down (700-800 loft I think) and have been toasty warm (perhaps a bit too warm for spring/autumn whilst between 3000m to 4000m), great if extended time around 5000m and above.

I really value their dryloft shells. Paddy's bag had dryloft lined hood and foot section too which I liked.

Check the cut of the bag suits you - try it on in the shop. One Planet feels a bit too spacious to me and some Western Mountaineering a bit too snug.

How many nights up high, how many in a tent, will you use it for Aussie winters, you might be able to get by with a less warm bag which will ultimately get more use.

Guys,
thank you very much, every reply was very useful.
BTW people who have done Nepal trekking recently told me were are very cheap and lightweight, starting from $50, down sleeping bags in Kathmandu. the only thing they are very bulky, but maybe you can squeeze it somehow.

On 24/01/2013 UILKA wrote:>Guys,>thank you very much, every reply was very useful. >BTW people who have done Nepal trekking recently told me were are very>cheap and lightweight, starting from $50, down sleeping bags in Kathmandu.>the only thing they are very bulky, but maybe you can squeeze it somehow.

If cost is an issue you can always hire? There's plenty of places in Kathmandu that hire and it saves having to carry around a massive bag if you're travelling somewhere else after. I hired my first trip there because I didn't want to be lugging a sleeping bag around through India.

On 24/01/2013 UILKA wrote:>Guys,>thank you very much, every reply was very useful. >BTW people who have done Nepal trekking recently told me were are very>cheap and lightweight, starting from $50, down sleeping bags in Kathmandu.>the only thing they are very bulky, but maybe you can squeeze it somehow.

yes you can buy sleeping bags in nepal for cheap prices. there are some good ones available too . you can also hire big thick ones. bulky and heavy doesnt really matter if you are only trekking and porter is carrying bag.

I've slept on the snow with a +5 bag and was a little cold. just had to wear all my clothes.:-)